The present invention relates to the qualitative and quantitative tracing of sewage flows and to the monitoring of reactions in fluids, with particular reference to biodegradation reactions in sewage treatment plants, to the monitoring of the operational efficiency of such plants and to the control thereof.
The need to trace sewage effluents in environmental water bodies, such as rivers, estuaries and coastal waters is self-evident but at present various difficulties are encountered in putting it into effect. For example colored tracers, which may be added to a flow to give rapid preliminary information on flow paths in nonturbid flows, are generally adsorbed on to solids suspended in sewage flows and hence give anomalous results, if any, under these conditions. Constituents of the sewage itself, such as potassium and sodium chlorides, although more difficult to assess than coloured tracers, are usable in fresh water conditions but, naturally, cannot be used as tracers in salt waters. Many other sewage constituents, such as urea, also occur naturally at levels similar to those found in sewage or have until now been very difficult or time-consuming to estimate.
One object of the invention is, therefore, to provide a more convenient method of tracing sewage flows than is currently available.
A further requirement in connection with sewage effluents is that of monitoring the outflows from sewage-treatment plants to ensure that the quantities of remaining pollutants are below statutory maximum levels.
At present two types of large-scale sewage-treatment plant are in widespread use and are known as activated sludge plants and biological filter plants respectively. In general terms, these plants include a primary treatment stage in which suspended solid particles are separated from liquid sewage and a secondary treatment stage in which the liquid is subjected to biodegradation to render it fit for discharge into the environment after a secondary filtration process for removing further suspended matter.
The operational efficiency of such plants is currently determined by BOD (biological oxygen demand) and COD (chemical oxygen demand) analyses on the effluent discharged, maximum allowable BOD and COD values being laid down for each plant according to the size and nature of the water body receiving the discharge.
Such BOD and COD values, however, are a combination of a large number of factors, requiring complex and time-consuming measurements, and a need has been felt for a simple method of obtaining reliable information on the basic processes at work in a sewage plant and on the operational efficiency of the plant.
After considerable research, it has been found possible to detect a selected sewage component by a simple reliable method which can be adapted for use in tracing sewage flows and it has also been found that the estimation of a single sewage component may be used in the monitoring of the operational efficiency of a sewage-treatment plant.